The ATM Forum UTOPIA L2 Technical Specification af-phy-0039.000 states that a maximum of 26 Physical Interface (PHY) addresses can be polled within one cell transfer of 53 bytes. This is assuming that the PHY can give a CLAV response within 1 clock cycle. If additional clock cycles are required for the PHY to respond to a PHY address, then less than 26 PHY addresses can be polling within one cell transfer.
The convention is to use single CLAV status polling to poll up to 31 PHY addresses, which is more than the maximum polling bandwidth of a single CLAV status signal. A common way of increasing the polling bandwidth is to add additional CLAV status signals to cover the number of PHY addresses being polled. However, this requires the PHY to support more than one CLAV signal. This is known as Multiple Status Polling (MSP). MSP does not address the issue that more PHY addresses may require polling than the maximum achievable polling bandwidth of one CLAV signal.
A master device generally has the task of polling the PHY addresses. A PHY address may return an active CLAV status indicating that it is ready for another transfer, unless this PHY is physically removed from the system. The CLAV status response for that specific PHY address will not change for successive polls until a cell has been transferred on that PHY address.
For each CLAV status signal, more PHY addresses may require polling than can be polled within one cell transfer period (e.g., 53 clock cycles). For example, a majority of PHY addresses may be deemed slow connection PHY addresses. Periodically, the latency of polling fast connection PHY addresses may exceed more than a cell period. For example, fast connection PHY addresses can indicate up to 100 CLAV statuses within a period of 2 successive slow connection CLAV statuses. By not checking the fast connection CLAV status often enough, the fast connection may become congested further back in a network. In addition, if all PHY addresses at one connection speed have indicated an active CLAV and have yet to be serviced, polling bandwidth will be wasted each time the connection speed, with no PHY addresses requiring polling, is selected by a polling arbiter.
When using Multiple CLAV status polling (MSP), where up to four independent PHY CLAV responses are received for each PHY address, CLAV polling optimization can only occur once all CLAV status for that PHY address are flagging an active CLAV status. Once any one of those CLAV statuses for that PHY address has been serviced where the CLAV status for that PHY address is unknown, then all CLAV statuses for that PHY address must be checked again.
MSP increases polling bandwidth by using more CLAV status signals. However, this requires the PHY to accept more than one CLAV status signal or multiple PHYs are required. If multiple CLAV status polling is performed, more than one PHY is polled per PHY address so each PHY address may have more than one CLAV status signal. When one PHY indicates an active CLAV status, the other PHYs using that PHY address may not yet have indicated an active CLAV status. This means the PHY addresses are polled again until all CLAV statuses for that PHY address indicate an active CLAV status and have yet to be serviced.
The UTOPIA device within a Helium 210 Chip may poll 31 PHY address in a method specified by the ATM forum UTOPIA L2 specification af-phy-0039.000. Using a single CLAV status polling method, each PHY address is polled in turn, starting at address 0x00 through to address 0x1E. The Null PHY address 0x1F is polled between each polled PHY address to allow the PHY to respond. The means that only 26 PHY addresses can be polled for every cell transferred (53 UTOPIA interface clock cycles). This polling limitation generally is difficult to overcome but the efficiency of the polling can be improved to ensure that only PHY addresses, which require polling, are polled.
Current technology implements three polling specs defined within the ATM forum UTOPIA L2 spec af-phy-0039.000. These polling specs are Single CLAV status polling; Multiplexed CLAV status polling (MSP) using 4 CLAV signals; and Direct CLAV status indication using four CLAV status signals.
Therefore, there is a need for a more efficient method and system for optimizing UTOPIA CLAV polling arbitration.